Abstract: Aiming at the discharge ablation fault of 5052 current transformer in a 500 kV substation, the causes of the fault were analyzed from the aspects of main chemical composition, fracture morphology, microstructure, microhardness and energy spectrum analysis. The results show that the arch surface of the transformer blasting piece was damaged by collision pressure during transportation or assembly, which made the blasting pressure and stability of the blasting piece significantly reduced. After the transformer operated under normal working conditions for three years, the arch surface of the blasting slice underwent instability reverse blasting, and cracking along the weakening groove, resulted in SF₆ leakage, reduced the insulation of the transformer, and then the discharge ablation fault occured.